The present invention relates broadly to a linear slide bearing for linearly guiding sliding parts such as those incorporated in NC lathes and other machine tools, industrial robots and so forth and, more particularly, to a construction for allowing an adjustment of the clearance between a track shaft and a sliding block constituting the linear slide bearing, thereby to suitably preload the load carrying balls between the track shaft and the sliding block or to smooth the running of these balls.
Generally, a linear slide bearing has a sliding block having a substantially inverted C-shaped cross-section with the lower side recessed to form a cavity which is adapted to receive the upper end portion of a shaft track with a suitable clearance held therebetween. The linear slide bearing further has a multiplicity of balls adapted to run along a plurality of endless ball passages formed in the sliding block. The balls carry the load applied to the sliding block in all directions, while guiding the linear reciprocating movement of the sliding block along the track shaft.
This type of linear slide bearing has to meet various requirements. For instance, this type of bearing has to be mounted in the sliding parts of ordinary industrial machines at a high precision, and to exhibit a high precision of positioning and reciprocation of the sliding parts, as well as a high durability. In order to meet these demands, it is necessary to keep, between the loaded ball groove in the sliding block and the loaded ball groove in the track shaft, a distance which is seemingly smaller than the diameter of the balls, thereby to preload the balls to ensure the uniform contact of all balls with the ball rolling surfaces of the loaded ball grooves, so as to eliminate any unfavourable effect such as the hammering action of the balls which may be caused by the inertia of the balls when they make a turn at each end of the loaded ball passage, and any twisting which may be caused by disorder of the balls. It is also necessary to provide suitable means for ensuring smooth running of the balls from the non-loaded region into the loaded region and vice versa.
For suitably preloading the balls, hitherto, such measures have been taken as to select the ball carefully so that the balls used in the bearing have strictly identical diameters. It has been also attempted to adjust the clearance between the sliding block and the track shaft by means of bolts which cooperate with slots formed in the sleeve portions of the sliding block.
On the other hand, it has been proposed to effect a so-called crowning, in which the loaded ball groove in the sliding block has a greater width at both its end portions than at its central portion, aiming at smoothing the running of the balls in the endless ball passage.
The careful selection of the balls, however, required an impractically long time and much-labor. In addition, since the selection of the balls and the adjustment of the clearance by adjusting means provided on the sliding block have to be made before the bearing is mounted in the sliding part of the machine, it is quite difficult to optimumly preload the balls in accordance with respective purposes of use of the bearing with these measures. The crowning, which requires a specifically high precision, is also quite troublesome and time consuming.